1. Field of the Invention
The present invention relates to an arrangement of power modules and an arrangement of capacitors provided inside a power conversion apparatus.
2. Background Information
Generally speaking, a main component of a power conversion apparatus (such as an inverter) is a power module, which is also called a switching module or a semiconductor module. The power module typically has two power transistors connected in series, and two diodes connected in antiparallel to the corresponding power transistors. The power module serves the important task of converting a direct current received from a power source into an alternating current and outputting the alternating current.
For example, Japanese Laid-Open Patent Application Publication No. 7-245968 discloses an inverter apparatus having a direct current input section comprising positive and negative terminals connected to a power source and a plurality of power modules arranged radially so as to be centered about the direct current input section. At least one power module is required for each phase of the alternating current. Thus, the number of power modules is at least equal to the number of phases of the alternating current. If the number of phases of the alternating current is three, then the power conversion apparatus has at least three power modules. When the power modules convert a direct current into an alternating current, the switching operation of the power modules causes high frequency ripple currents to occur. Additionally, surge voltages occur when the power modules are turned off. Therefore, it is necessary to provide a capacitor to smooth the ripple currents and to absorb the surge voltages.
In the inverter apparatus described in the above mentioned reference, the direct current input section of each power module is formed as an integral unit with positive and negative electrodes being separated by an insulating layer, and arranged on an upper portion of the power module. A plurality of capacitors are provided so that one capacitor is arranged on an upper portion of the electrodes of each power module and connected such that the impedance between the power module and the capacitor is low. This arrangement provides a compact power conversion apparatus with low impedance between the power modules and capacitors.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved power conversion apparatus and motor drive system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.